The March/April issue of Composites Manufacturing magazine has an article titled, Composites: No Longer the Odd-Component Out, which features an overview of how automotive OEMs are implementing the use of composites as light weight solutions for future vehicles. As a bonus for our online readers, here is an online exclusive that coincides with the article.
Below, Christian Buhlmann, spokesman for Volkswagen and Volkswagen Products in the Americas, shares a behind-the-scenes look at the production process for the Volkswagen XL1. Approximately 21 percent of the car is made of CFRP (carbon fiber reinforced polymer). According to Bulmann, “For the decisions we made [when designing the XL1], it is important to understand the entire production process.”
Production Stage I – Bodyshell Frame
Production of the XL1 begins with delivery of the CFRP monocoque, which is produced by a supplier in Austria using resin transfer molding (RTM). The manufacturing process itself was developed over several years in close cooperation with Volkswagen. In Osnabrück, the monocoque is mounted to an assembly support plate; this is where the body is built – but without doors or lids. This first body production stage is referred to as the “bodyshell frame.” At this station, all parts are moved to their prescribed design positions by special fixtures. This approach is necessary to maintain the tight manufacturing tolerances.
The various interior and exterior surfaces of the monocoque itself are pretreated in advance. This pretreatment is required to attain tight gaps and smooth surfaces. In the interior of the XL1, many of the CFRP surfaces were intentionally left uncovered by trim panels, and so the high-tech material remains visible. The individual CFRP components are joined to one another in the bodyshell frame by gluing – a highly complex and unique process in manufacturing technology. The operation of mounting the roof section to the monocoque illustrates just how complex this process is.
Unlike welded metal parts, the roof of the XL1 cannot simply be placed on the monocoque. Rather the strength of the adhesive material must compensate for all fit gaps of the monocoque-roof side member structure and the different material thicknesses of the laminated roof. Therefore, this part is made to hover over the monocoque before gluing. The gluing process itself is performed according to a precisely defined sequence with precisely defined curing times.
Over the course of production stage I, the boot pan is brought into position with the water channel, and it is glued and screw fastened. In addition, all structural and exterior skin parts (rear cross members, rear termination part, side panels front and rear) are positioned and screwed via a sled fixture. Last but not least, employees check and document the dimensional tolerances of the entire assembly as the final step of every production stage. Each individual part of the XL1 is also documented with a serial number and its production history.